The invention relates to a non-reciprocal optical element, particularly for use as an isolator or circulator, which is connected to at least two monomode optical waveguides and which has a magneto-optical waveguide structure intended to be subjected to a transversal magnetic field directed perpendicular to the direction of propagation of the optical wave.
Such a differential phase shift circulator/isolator in the structure of an optical strip line is known from "Applied Optics", Vol. 23, 1984, pp. 1886 to 1889. The incident light wave is split up into two equal parts for which purpose Y couplers or hybrid couplers are used. The two sub-waves traverse various parallel channels of the magneto-optical waveguide structure which is constructed in such a way that an optical path difference of .lambda./4 is produced at the entrance of the secound coupler, which difference corresponds to a phase difference of .pi./2. Additionally, non-reciprocal phase shifts in the two channels of -.pi./4 and +.pi./4 are generated by corresponding transversal magnetic fields so that for one light direction the optical phase difference of .pi./2 is just compensated but is supplemented to .pi. for the opposite light direction. Based on this principle, isolators and circulators can be constructed dependent on the arrangement of the waveguides and the couplers.
The known arrangement is elaborate and particularly has a relatively large construction length determined by two separate couplers (Y or hybrid) which must be connected to the magneto-optical waveguide structure. High losses arise.